United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-43: Problems with Silver Zeolite Sampling of Airborne Radioiodine

                                                          SSINS No: 6835  
                                                          IN 86-43         

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, DC 20555

                                June 10, 1986

Information Notice No. NO 86-43:   PROBLEMS WITH SILVER ZEOLITE SAMPLING OF 
                                   AIRBORNE RADIOIODINE 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP) 

Purpose: 

This information notice is provided to alert licensees of the potential 
hazards associated with sampling for radioiodines with silver zeolite (AgZ) 
in the presence of hydrogen (H2) and oxygen (02)  It is expected that 
recipients will review the information for applicability to their radiation 
monitoring and survey program and consider actions, if appropriate, to 
preclude similar problems at their facility However, suggestions contained 
in this notice do not constitute NRC requirements; therefore, no specific 
action or written response is required 

Description of Circumstances: 

During a recent surveillance test, the LaCrosse Boiling Water Reactor (BWR) 
experienced a hydrogen ignition while sampling the plant offgas system The 
high H2 concentration in the offgas system was caused by a faulty H2-02 
recombiner An excerpt from the NRC regional followup inspection report in 
Attachment 1 gives a detailed account of the event 

The licensee believes that the ignition source during this event was the AgZ
cartridge used in the offgas sampling rig The cartridge contained 
dehydrated (less than 1% water content) AgZ The heat of hydration released 
when the AgZ absorbed moisture from the sample stream may have added enough 
heat to allow catalytic recombination of H2 and 02 Catalysis also releases 
heat that would have rapidly increased the temperature of the AgZ to the H2 
ignition point 

Discussion: 

Silver zeolite cartridges are used for sampling radioiodines in radioactive 
gas mixtures The AgZ chemically traps the iodines while letting the noble 
gasses (which would interfere with subsequent radioanalysis) pass through 
The LaCrosse event highlights the following two properties of AgZ that are 
apparently not well understood by the industry 



8606040009  


                                                            IN 86-43       
                                                            June 10, 1986  
                                                            Page 2 of 3    

1   Hydration State 

     The noble gas retention efficiency of AgZ is a function of its water 
     content (hydration) Dehydrating AgZ activates its surface, freeing-up 
     sites for noble gas adsorption Data presented in NUREG/CR-3445 (March,
     1985), "A Comparison of Iodine, Krypton, and Xenon Retention 
     Efficiencies for Various Silver Loaded Adsorption Media," show that the
     retention efficiency for bound noble gas (gas not residing in the void 
     fraction of AgZ) of dehydrated AgZ is an order of magnitude higher than
     AgZ hydrated to 9% by weight Because AgZ is used to minimize noble gas
     retention and interference, the use of dehydrated AgZ is 
     self-defeating 

     The heat of hydration can also effect AgZ's iodine retention Heat 
     released, if dehydrated AgZ is used to sample humid air, increases its 
     temperature This elevated temperature can reduce the retention 
     efficiency for iodine 

     For the above reasons, when sampling for airborne radioiodine in the 
     presence of noble gases, use of dehydrated or activated AgZ is not 
     appropriate 

2   Catalytic Properties 

     Silver zeolite will act as a catalyst to recombine H2 and 02 into H20 
     (water) One manufacturer's study, run with 2% H2 in moderately dry 
     (10% humidity) air, indicated a threshold temperature at 150F 
     before the catalytic reaction becomes significant Although the 
     dependence of this threshold temperature on such parameters as moisture 
     content and H2 concentration are not known, it is assumed that higher 
     H2 concentration will lower the threshold temperature This catalytic 
     property of AgZ makes its use in sampling from explosive or potentially 
     explosive atmospheres (such as BWR offgas or waste gas storage tanks) 
     unadvisable 

Note that for sampling the offsite environment or other onsite areas where 
there is no possibility of having a significant H2 concentration, the 
catalytic properties of AgZ are of no concern 

In addition to returning the offgas recombiner to an operable state, the 
licensee is considering the following actions: 

o    using only charcoal cartridges for sampling the offgas radionuclides 

o    using a portable H2 analyses and checking for H2 concentration before 
     sampling the offgas 

o    using only partially hydrated (or noncatalyzing cartridges) for 
     post-accident sampling of stack effluents 

o    not using AgZ for post-accident containment sampling unless H2 
     concentration is less than 4 percent  


                                                            IN 86-43  
                                                            June 10, 1986  
                                                            Page 3 of 3 

No specific action or written response is required by this information 
notice If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office 


                                   Edward L Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contacts: Roger L Pedersen, IE 
                    (301) 492-9524 

                    Edward F Williams, IE 
                    (301) 492-7611 

Attachments:
1   Hydrogen Ignition in an Offgas Sampling Rig 
2   List of Recently Issued IE Information Notices  


                                                            Attachment 1   
                                                            IN 86-43       
                                                            June 10, 1986  
                                                            Page 1 of 2    

                 HYDROGEN IGNITION IN AN OFFGAS SAMPLING RIG
        (Excerpted from Referenced Inspection Report, Edited Version)

On March 6, 1986, a senior health physics technician at the LaCrosse Boiling
Water Reactor set up a portable sampling system to sample particulate and 
radioiodine activity in the operational offgas line both upstream and 
downstream of the on-line offgas system final high-efficiency particulate 
air (HEPA) filter and charcoal adsorber bank The sampling was being 
conducted to test the collection efficiency of the HEPA filter and charcoal 
adsorber using a differential radionuclide concentration method 

The sampling equipment consisted of new tygon tubing, a flow meter, an 
aluminum filter paper holder containing an acetate filter paper, and a dual 
cartridge holder containing two plastic cartridges containing silver zeolite
(AgZ) The AgZ had been dehydrated by the manufacturer to less than 5 
percent moisture Past sampling of the offgas line was performed using two 
standard 2-inch charcoal cartridges instead of AgZ cartridges AgZ 
cartridges were substituted because they adsorb less noble gaseous activity 
than charcoal cartridges and, therefore, reduce sample analysis 
interferences 

Two minutes after starting the sampling equipment (flow rate of 06 cfm), 
the technician noted that water droplets had formed on the inside of the 
tygon tubing downstream of the filter holders One minute later, the 
technician heard a loud bang and saw a bluish flash inside the sample 
tubing The technician then turned off the sampling pump, isolated the 
sampling lines, and inspected the sampling equipment The tygon tubing was a 
burnt brown color; the inside of the flow meter was covered with a 
brown-colored oil film; the cartridge holder was hot, difficult to open, and 
had a burned odor when opened; plastic parts of the zeolite filters and 
holder displayed some melting and were fused; the plastic retaining screens 
in the zeolite holders were no longer intact; and the HEPA filter had 
disintegrated 

The licensee believes that an ignition began in the sample holder and that 
sufficient H2, must have been present in the sample lines to sustain an 
ignition Sufficient H2 could be present if the offgas system catalytic 
recombiner, located upstream of the filters being tested, were not operating
optimally There is no H2 monitor downstream of the catalytic recombiner 
The licensee's Radiation Protection Engineer discussed the potential of H2 
and O2 recombination catalysis by AgZ at ambient temperatures with two 
outside suppliers It was determined that dehydrated AgZ will absorb 
moisture from the sample stream until it reaches hydration During this 
hydration, which creates a slightly exothermic reaction, the AgZ granules 
will heat up During this heating, additional H2 and 02 alignment with the 
AgZ molecules may occur, and some controlled catalytic recombination also 
may occur, which may further increase the AgZ granules temperature At about 
150 F, the AgZ will reach its threshold temperature for H2 and 02 catalytic 
recombination At this threshold temperature, the AgZ may cause a rapid 
recombination (ignition) of H2 and 02 if the H2 concentration is above 4 
percent This may rapidly generate temperatures inside the AgZ in excess of 
1065F 



                                                            Attachment 1   
                                                            IN 86-43       
                                                            June 10, 1986  
                                                            Page 2 of 2    

The offgas system continued to operate after the ignition There were 
fluctuations in effluent noble gas, particulate, and halogens for several 
hours after the ignition; however, no alert setpoint was reached The 
licensee noted an increase in the temperature of the offgas storage tanks 
and the catalytic recombiner (monitored parameters) The system slowly 
returned to near normal except that an identifiable increase in halogen and 
particulate effluent remained These remaining increases indicate a possible
degradation of the final HEPA filter and charcoal adsorber The licensee 
plans to inspect the filter bank for damage and replace the HEPA and 
charcoal as necessary during this outage 

Reference: 

LaCrosse Boiling Water Reactor Inspection Report No 50-409/86003 (DRSS), 
March 28, 1986 


Page Last Reviewed/Updated Tuesday, November 12, 2013